B-F bond length in BF3 is shorter than B-F bond length in (BF4)- why?

B-F bond length increases when BF₃(130 pm) reacts with F- to form (BF₄)- [143 pm]. Its due to absence of Back-bonding in (BF₄)- hence B-F bond has completely single bond character

What is structure of solid Ortho Boric acid ?

Boric acid mainly exist in polymeric form like tri ,tetra, panta but tri and tetra meta boric acid are well known, because it's sodium salt (sodium borate,or sodium tetra borate or disodium tetra borate) is very famous which is called "Borax" or Tincal and commercially named as Jeweller,s of Borax [Na₂B₄O₅(OH)₄•8H₂0 or Na₂B₄O₇•10H₂O]

In solid state Boric [B(OH₎₃] unit are hydrogen bonded together into two dimensional sheet.

Borax is uses in manufacturing of ENAMELS and glazes for pottery and disinfectant in medicine.

Related Questions:

What are Silicones? explain with examples.

What are "pyro" oxy acids?

What are "Ortho" or "Meta" oxyacids?

What is Meta Boric Acids?

What are the structural difference between oxides ( P4O6 and P4O10) of phosphorous?

What are common structural features of oxides (P4O6 and P4O5) of phosphorous?

What are most common cyclic meta silicates?What is "calgon" ? Give structure and its uses?

What are the Silicones? Give one example one cyclic Silicone?What is the structure of trimetaboric acid and trimetaborate ion?

What is the structure of trimetaboric acid and trimetaborate ion?

Related Questions:

What are Silicones? explain with examples.

What are "pyro" oxy acids?

What are "Ortho" or "Meta" oxyacids?

What is Meta Boric Acids?

What are the structural difference between oxides ( P4O6 and P4O10) of phosphorous?

What are common structural features of oxides (P4O6 and P4O5) of phosphorous?

Why Borazine is more reactive than benzene towards Electrophic Aromatic substitution reactions ?

 In Borazine molecule, nitrogen is more electro negative than the boron. Nitrogen acquires partial negative charge and boron acquires partial positive charge and back bonding take place between boron and nitrogen. And it is more reactive as compared with Benzene, because Borazol is less stable and more reactive toward Electrophilic Aromatic Substitution reactions due to high polarity of B-N bonds borazine molecule while in benzene all bonds are non polar.

                                 Borazine 

Why Borazine (B3N3H6) is also known as inorganic benzene ?.

Borazine (B3N3H6) is also known as inorganic benzene due to its resemblance in structure and properties with benzene like.

(1) Both are cyclic with alternative double bond.

(2) Both are aromatic in nature.

(3) Both are give electrophilic substitution reactions.

 

Related Questions:

Why Ga has small size than Al exceptionally

Why aqueous solution of borax reacts with two moles of acids ?

What is structure of solid Ortho Boric acid ?

What is the structure of trimetaboric acid and trimetaborate ion?  

Why Borazine is more reactive than benzene towards Electrophic Aromatic substitution reactions ?

Why Borazine (B3N3H6) is also known as inorganic benzene ?.

Why B-F bond length in BF3 is shorter (130 pm) than B-F bond Iength in BF4- (143 pm)?. Explain.

Why B-F do not exist as dimer?. Explain.

Although anhydrous aluminium chloride is covalent but its aqueous solution is ionic in nature. Why?

Why Boric acid become strong acid in the presence of cis 1,2-diol or 1,3-diol ?

Why B-F bond length in BF3 is shorter (130 pm) than B-F bond Iength in BF4- (143 pm)?. Explain.

BF₃ has a planar trigonal geometry due to sp2 hybridisation of boron in BF₃. Boron atom in BF3 is electron defficient (incomplete octet) and fluorine atom is electron rich (due to the presence of three lone pair of electrons on fluorine atom).

Boron and fluorine both belong to the same period. Hence their bonding orbitals have almost same size  and same energies.Thus Back Bonding takes place between B and F. This introduces a partial double bond  character between B-F of BF3. Thus B-F bond length decreases from normal B-F bond length.

 In BF₄^-,the  hybridization of boron is sp3. The B-F bond has pure single bond character. Thus B-F bond length in BF₄^-, is more than the B-F bond length in BF₃ .

 Related Questions: 

Why aqueous solution of AlCl3 is acidic in nature ?

What happen when aq AlCl3 react with Acid or Base?

Although anhydrous aluminium chloride is covalent but its aqueous solution is ionic in nature. Why?

Why BF3 do not exist as dimer?. Explain.

Why B-F bond length in BF3 is shorter (130 pm) than B-F bond Iength in BF4- (143 pm)?. Explain.

B-F bond length in BF3 is shorter than B-F bond length in (BF4)- why?

When B2H6 is allowed to react with following Lewis bases, then how may given Lewis base form adduct through symmetrical Cleavage of B2H6.

What is product of reaction between diborane (B2H6) and ammmonia (NH3)?

Why methylation of Diborane (B2H6) replace four hydrogen only ?

What is Use of Boric Acid?

What is use of Orthoboric acids?

What is basicity of "Boric acid" ?

Why Boric acid exist in solid state ?

What is structure of solid Ortho Boric acid ?

What is effect of heat on Borax?

What is the structure of trimetaboric acid and trimetaborate ion?

What is the Sodium per borate ,give the structure and its uses?

Why aqueous solution of borax reacts with two moles of acids ?

What is the molecular formula of Borax ?

Why Boric acid become strong acid in the presence of cis 1,2-diol or 1,3-diol ?

Why Borazine is more reactive than benzene towards Electrophic Aromatic substitution reactions ?

Why Borazine (B3N3H6) is also known as inorganic benzene ?.

Four-center two-electron bond (4C-2e Bond): Structure of AlCl3:

What is the difference between the structure of AlCl3 and diborane?

Why BF3 do not exist as dimer?. Explain.

Baron trihalides do not undergo dimerisation, due to small size of boron atom which is unable to form bonds with more than three large halogen atoms. BX3 molecules are also stabilized by back bonding. 

 

Related Questions:

Why Ga has small size than Al exceptionally

Why aqueous solution of borax reacts with two moles of acids ?

What is structure of solid Ortho Boric acid ?

What is the structure of trimetaboric acid and trimetaborate ion?  

Why Borazine is more reactive than benzene towards Electrophic Aromatic substitution reactions ?

Why Borazine (B3N3H6) is also known as inorganic benzene ?.

Why B-F bond length in BF3 is shorter (130 pm) than B-F bond Iength in BF4- (143 pm)?. Explain.

Why B-F do not exist as dimer?. Explain.

Although anhydrous aluminium chloride is covalent but its aqueous solution is ionic in nature. Why?

Why Boric acid become strong acid in the presence of cis 1,2-diol or 1,3-diol ?

Although anhydrous aluminium chloride is covalent but its aqueous solution is ionic in nature. Why?

Aluminium forms covalent compound with chloride because lonisation enthalpy (∆iH= +5137 kJ/mole) of Aluminium is very high due to small size and chlorine is unable to convert  Al into Al⁺³ ions. 

However, when anhydrous AlCl₃ (which is covalent in character) is dissolved in water, it undergoes hydration as follow:  

 Al₂CI₆ + H₂O --> 2[Al(H₂O)₆]⁺³ + (∆H)  

Hydration of anhydrous aIuminium chloride is highly exothermic in nature. The hydration enthalpy is more than ionisation enthalpy of aluminium.This hydration enthalpy removes all the three valence electrons of the aluminium leading to the formation of Al³⁺ more easly.This AI³⁺ is hydrated with water and form a complex ion. Thus in water Al exist as [Al(H₂O)₆]⁺³ . The three electrons of aluminum is accepted by CI of AlCl₃. Thus hydrated AlCl₃  represented [Al(H₂O)₆]Cl₃   and it is ionic in nature.

Related Questions: 

(1) Although anhydrous aluminium chloride is covalent but its aqueous solution is ionic in nature. Why?

(2) Why Ga has small size than Al exceptionally

(3) Why aqueous solution of borax reacts with two moles of acids ?

(4) What is structure of solid Ortho Boric acid ?

(5) What is the structure of trimetaboric acid and trimetaborate ion?  

(6) Why Borazine is more reactive than benzene towards Electrophic Aromatic substitution reactions ?

(7) Why Borazine (B3N3H6) is also known as inorganic benzene ?.

(8) Why B-F bond length in BF3 is shorter (130 pm) than B-F bond Iength in BF4- (143 pm)?. Explain.

(9) Why B-F do not exist as dimer?. Explain.

(10) Although anhydrous aluminium chloride is covalent but its aqueous solution is ionic in nature. Why?

(11) Why Boric acid become strong acid in the presence of cis 1,2-diol or 1,3-diol ?

(12) Four-center two-electron bond (4C-2e Bond): Structure of AlCl3:

(13) What is the molecular formula of Borax ?

(14) What is the difference between the structure of AlCl3 and diborane?

Why Boric acid become strong acid in the presence of cis 1,2-diol or 1,3-diol ?

Boric acid is a weak monoprotic acid (Ka=6.4×10⁻¹⁰).Therefore, it cannot be directly titrated with standard strong alkali (NaOH). But by the addition of an organic poly hydroxy compound such as 1,2- or 1,3-diol, (Like Sugar, Mannitol, Catechol)  it is converted to a much stronger acid, which can be titrated using phenolphthalein. This is due to the complex formation between hydrated borate ion and either 1,2- or 1,3-diol  for example .

Ploy hydroxy (Cis-diol) increases acidity of boric acid due to formation of complex with metaborate and reaction goes to farward to produce more H⁺.

What is the molecular formula of Borax ?

(A) Na₂[B₄O₃(OH)₄].6H₂O

(B) Na₂[B₄O₅(OH)₄].6H₂O

(C) Na₂[B₄O₅(OH)₄].8H₂O

(D )Na₂[B₄O₆(OH)₂].8H₂O

The structure of Borax is Na₂[B₄O₅(OH)₄].8H₂O.

Hence option (C) is the correct answer for details click on link given below

Tincol or Suhaga:

Three-center four-electron Bridge bond (3C-4e Bond): Structure of AlCl3:

(1) Al₂Cl₆ is neither hypovalent nor hypovalent rather its octet is complete. We will used  MOT here  it cannot act as Lewis acid  due to crowding in spite having vacant d orbital’s   however AlCl₃  act as Lewis acid .

(2) Al₂Cl₆ contains six bonds having two bridge bonds (3c-4e) and four bonds is (3C-4e) bridge bonds are lies perpendicular to plane.

(3) The bond lengths of terminal Al−Cl bonds are shorter (206 pm) while bond length of bridged Al−Cl bonds are longer (221 pm) and also outer bond angle (Cl−Al−Cl) are greater (118) than inner bond angle (Al−Cl−Al).

(4) Maximum six atoms are lies in same plane which four terminal Cl and two aluminium atoms.

(5) AlCl₃ in vapor phase or in non-polar solvent is dimeric Al₂Cl₆ hence sp3 hybridised having 3c-4e bonds.

Related Questions: 

(1) Why aqueous solution of AlCl3 is acidic in nature ?

(2) What happen when aq AlCl3 react with Acid or Base?

(3) Although anhydrous aluminium chloride is covalent but its aqueous solution is ionic in nature. Why?

(4) Why BF3 do not exist as dimer?. Explain.

(5) Why B-F bond length in BF3 is shorter (130 pm) than B-F bond Iength in BF4- (143 pm)?. Explain.

(6) B-F bond length in BF3 is shorter than B-F bond length in (BF4)- why?

(7) When B2H6 is allowed to react with following Lewis bases, then how may given Lewis base form adduct through symmetrical Cleavage of B2H6.

(8) What is product of reaction between diborane (B2H6) and ammmonia (NH3)?

(9) Why methylation of Diborane (B2H6) replace four hydrogen only ?

(10) What is Use of Boric Acid?

(11) What is use of Orthoboric acids?

(12) What is basicity of "Boric acid" ?

(13) Why Boric acid exist in solid state ?

(14) What is structure of solid Ortho Boric acid ?

(15) What is effect of heat on Borax?

(16) What is the structure of trimetaboric acid and trimetaborate ion?

(17) What is the Sodium per borate ,give the structure and its uses?

(18) Why aqueous solution of borax reacts with two moles of acids ?

(19) What is the molecular formula of Borax ?

(20) Why Boric acid become strong acid in the presence of cis 1,2-diol or 1,3-diol ?

(21) Why Borazine is more reactive than benzene towards Electrophic Aromatic substitution reactions ?

(22) Why Borazine (B3N3H6) is also known as inorganic benzene ?.

(23) Four-center two-electron bond (4C-2e Bond): Structure of AlCl3:

(24) What is the difference between the structure of AlCl3 and diborane?

What is the difference between the structure of AlCl3 and diborane?

The hydrogen bridged dimer B2H6 contains two three centre (3C-2e bond), two electron bonds, A three-centre bond uses two electron to link three atoms, and  four two centre, two electron bond (2C-2e). 3C-2e bridge bond is perpendicular to plane in which 2C-2e bond present.

In contrast the bridge bonding in Al₂Cl₆ contains two three centre (3C-4e bond), four electron bonds  which can be described in terms of electron pair bond in which a chlorine atom bonded to one aluminium atom act as a Lewis base by donating a lone pair of electrons to the aluminium atom which acts as a Lewis acid.

Related Questions: 

(1) Why aqueous solution of AlCl3 is acidic in nature ?

(2) What happen when aq AlCl3 react with Acid or Base?

(3) Although anhydrous aluminium chloride is covalent but its aqueous solution is ionic in nature. Why?

(4) Why BF3 do not exist as dimer?. Explain.

(5) Why B-F bond length in BF3 is shorter (130 pm) than B-F bond Iength in BF4- (143 pm)?. Explain.

(6) B-F bond length in BF3 is shorter than B-F bond length in (BF4)- why?

(7) When B2H6 is allowed to react with following Lewis bases, then how may given Lewis base form adduct through symmetrical Cleavage of B2H6.

(8) What is product of reaction between diborane (B2H6) and ammmonia (NH3)?

(9) Why methylation of Diborane (B2H6) replace four hydrogen only ?

(10) What is Use of Boric Acid?

(11) What is use of Orthoboric acids?

(12) What is basicity of "Boric acid" ?

(13) Why Boric acid exist in solid state ?

(14) What is structure of solid Ortho Boric acid ?

(15) What is effect of heat on Borax?

(16) What is the structure of trimetaboric acid and trimetaborate ion?

(17) What is the Sodium per borate ,give the structure and its uses?

(18) Why aqueous solution of borax reacts with two moles of acids ?

(19) What is the molecular formula of Borax ?

(20) Why Boric acid become strong acid in the presence of cis 1,2-diol or 1,3-diol ?

(21) Why Borazine is more reactive than benzene towards Electrophic Aromatic substitution reactions ?

(22) Why Borazine (B3N3H6) is also known as inorganic benzene ?.

(23) Four-center two-electron bond (4C-2e Bond): Structure of AlCl3:

(24) What is the difference between the structure of AlCl3 and diborane?

Titration of Borax: Tincal : Suhaga :

When Borax dissolved in water, it is subject to completely dissociate, and then, hydrolyzes to orthoboric acid (B(OH)₃  and [B(OH)₄]^- anions,  and resulting PH  of  solution about 9.13.

According to the equation:

Na₂[B₄O₅(OH)₄]⋅8H₂O(s)⟶2Na⁺(aq) + B₄O₅(OH)₄²⁻ (aq) + 8H₂O(l)

B₄O₅(OH)₄²⁻(aq) + 5H₂O(l) ⟶ 4 B(OH)₃(aq) + 2OH⁻(aq)

The liberated B(OH)₃(aq)  acts as a Lewis acid on OH⁻ ions from auto ionization of water, and hence, in equilibrium with water:

B(OH)₃(aq)+2H₂O(l) ⟶ B(OH)₄⁻(aq) + H₃O⁺(aq)

Therefore, one mole of borax reacts with two moles of strong acid solutions. This is  because when Borax dissolved in water Both B(OH)₃(aq)  and B(OH)₄⁻(aq) are formed but only  B(OH)₄⁻(aq) react with acid.  

For example:

                Na₂[B₄O₅(OH)₄].8H₂O(aq) + 2HCl(aq) ⟶ 4B(OH)₃(aq)+ 2NaCl (aq) + 5 H₂O

ILLUSTRATIVE EXAMPLE: Aqueous solution of borax reacts with two moles of acids.

This is because of:

(A) Formation of 2mol of B(OH)₃ only

(B) Formation of 2mol of Na[B(OH)₄]¯ only

(C) Formation of 1mol each of B(OH)₃ and Na[B(OH)₄]¯

(D) Formation of 2mol each of Na[B(OH)4]¯and B(OH)₃ of which only Na[B(OH)₄]¯ reacts with acid.

Answer: (D)

Solution: 

 Na₂B₄O₇ + 7H₂O ⟶ 2B(OH)₃ + 2Na[B(OH)₄]

B(OH)₃ or H₃BO₃ is an acid and does not react with acid. Hence Na[B(OH)₄] reacts with acid.